Device for the suction filtration of fluids

ABSTRACT

The invention relates to a device for the suction filtration of fluids, such as urea solutions for exhaust gas after-treatment systems, comprising a tank ( 2 ) storing the fluid, and a filter element ( 34 ) arranged therein provided with a filter medium ( 32 ), which separates the tank contents from a clean-side inner filter cavity ( 20 ) and extends from the bottom area ( 10 ) of the tank ( 2 ) to a filling level height ( 28 ), which corresponds to a part of the filling volume of the tank ( 2 ). On the filter cavity ( 20 ), a suction connection ( 22 ) is provided, via which the cleaned fluid can he discharged by way of a suction pressure corresponding to a system operating pressure. The invention is characterized in that the filter element ( 34 ) is provided with a filler medium ( 32 ), which is air-impermeable if suction pressures are within the range of a low system operating pressure.

The invention relates to a device for the suction filtration of fluids,such as urea solutions for exhaust gas after-treatment systems,comprising a tank storing the fluid, and a filter element arrangedtherein, provided with a filter medium, which separates the tankcontents from a clean-side inner filter cavity and extends from thebottom area of the tank to a filling level height, which corresponds toa part of the filling volume of the tank, wherein on the filter cavity,a suction connection is provided, via which the cleaned fluid can bedischarged by way of a suction pressure corresponding to a systemoperating pressure. The invention further relates to a filter elementprovided for use with such a device.

Devices for the suction filtration of fluids, such as liquid operatingmeans, fuels or the like, are used in widely different fields. Due tothe increasing requirements related to the emission behavior of internalcombustion engines, there has been an increased use more recently ofexhaust gas after-treatment systems with which for a selective catalyticreduction of nitrogen oxides, an aqueous urea solution, which is storedin a tank, is injected into an exhaust gas stream, in order, inconjunction with an SCR catalytic converter, to extract ammonia as theactual reducing agent. The urea solution can be obtained under the tradename “Adblue” at gas stations as an additional operating fluid for motorvehicles, for filling the respective storage tank. High demands areplaced on the purity of the urea solution for the operational safety ofthe associated injector system. Impurities can lead to blockages ofchannels and/or dosing pumps and/or valves in the injector system.Because the urea solution provided for filling can contain differentimpurities, and because, in particular, the danger also exists thatduring the filling process a quantity of contaminant may be introducedinto the tank, it is necessary to filter the urea solution which isdrawn from the tank.

For this purpose, a device of the aforementioned kind is known from thedocument WO 2011/124637 A1, in which the filter element serving as asuction filter is integrated into the tank storing the urea solution.The operating behavior of this device is not optimal for use in motorvehicles. Thus, the safe operation of the system depends on the fillinglevel height in the tank not falling below the upper edge of the filtermedium of the filter element. As soon as this is the case, there is thedanger that air is suctioned out of the tank via the unused, i.e.exposed, part of the filter medium, and passes into the system. For auseful operation of motor vehicles, however, it must be required thatthe filling level height is able to be lowered down to the bottom areaof the tank, in order in this way to remove a large fill quantity fromthe tank.

In view of these problems, the object of the invention is to provide adevice for suction filtration which, with a filter element integrated inthe respective tank, is distinguished by a highly favorable operatingbehavior.

This object is achieved according to the invention by a device which hasthe features of claim 1 in its entirety.

According to the characterizing portion of claim 1, an essential featureof the invention is that the filter element has a filter medium, whichis air-impermeable if suction pressure lies within the range of a lowsystem operating pressure. This avoids the danger that, as soon as thefilling level in the tank has fallen below the level of the upper edgeof the filter medium, such that a part of the filter medium above thefluid level is exposed, air is suctioned out of the tank via the filtermedium into the clean-side inner filter cavity. Without the entry ofair, practically the entire volume of the tank surrounding the filterelement can be used.

In particularly advantageous exemplary embodiments of the invention, thesuction connection on the filter cavity is disposed at the upper endthereof remote from the tank bottom. This arrangement not onlyeliminates the problem that during ongoing operation, air could besuctioned in when the fill level falls below the upper edge of thefilter element, but furthermore also guarantees a particularly safestart-up of the system after periods of downtime. Because the filtermedium is not air permeable, air initially located within the filtercavity of the filter element does not escape as the tank is filled.During startup of the pump, the quantity of air contained in the filterelement is discharged via the head-side suction connection. Because nourea solution is also discharged with this process, the quantity of aircan be eliminated using normal ventilation processes, for exampleself-actuated pump venting, after which the system is ready to operatefree of air. This ventilation process can occur automatically afterfilling processes.

An air-impermeable filter medium for the pressure gradient in questioncan be formed from a melt-blown fiber material, wherein plastic fibersmade, in particular, of PA 66, can be provided.

In particularly advantageous exemplary embodiments, a filter medium isprovided having a wall thickness in the range of 5 mm and a filterfineness in the range of 10 μm. In the case of filter media constructedin such a manner, the filter medium, as a result of the capillaryeffect, is completely suctioned full with the relevant fluid, even ifparts of the filter medium lie above the fill level, such that thefilter medium is air-impermeable for low suction pressures over theentire height thereof.

The subject matter of the invention according to claim 6, is also afilter element, which is provided for use with a device for suctionfiltration with one of the claims 1 to 5.

The invention is explained in greater detail below based on an exemplaryembodiment shown in the figure. They show in:

FIG. 1 a highly simplified functional sketch of the device according tothe prior art for suction filtration of a urea solution, wherein thefilling level height in the associated tank lies above the upper edge ofthe filter element;

FIG. 2 a representation of the device of the prior art according to FIG.1, wherein the filling level height is located below the upper edge ofthe filter element;

FIG. 3 a sketch representation, similar to FIGS. 1 and 2, of anexemplary embodiment of the device according to the invention forsuction filtration, wherein an operating state before start-up is shown;

FIG. 4 a corresponding sketch representation of the exemplary embodimentof the invention, wherein a state after start-up is shown, and

FIGS. 5 and 6 corresponding sketch representations, showing states ofthe exemplary embodiment of the invention with fill level heights in thetank lowered to different degrees.

The invention is described below based on an example that is providedfor the suction filtration of an aqueous urea solution, as is knownunder the name “Adblue”, and which can be used for exhaust gasafter-treatment systems of internal combustion engines. The invention isbased on the relevant prior art documented in WO 2011/124637 A1, as isrepresented in FIGS. 1 and 2, principally in the manner of simplifiedfunction sketches. The figures show a simplified representation of atank, identified by 2, which holds a supply of the urea solution. Afilter element 4 serving as a suction filter is disposed within thecircular cylindrical interior of the tank 2 in such a manner that itforms an inner cylinder, which is disposed on the bottom 10 of the tank2, concentric to the side walls 6 and 8 of the tank 2. The filter medium12 of the filter element 4 extends from a base plate 14 lying on thetank bottom 10, to a cover plate 18 located at the upper edge 16 of thefilter element 4, and, with base plate 14 and cover plate 18, delimitsan inner filter cavity 20 forming the clean-side during the filtrationprocess. Located on the base plate 14 is a suction connection 22, fromwhich a cleaned urea solution can be discharged via an opening 24 in thetank bottom 10, as indicated with flow arrows 26.

FIG. 2, in contrast to FIG. 1, illustrates an operating state of thedevice of the prior art, in which the filling level height 28 in thetank 2 has fallen below the upper edge 16 of the filter element 4. Assoon as this occurs during the operation of the device, and therebyexposes a part of the filter medium 12 in the airspace of the tank 2,air is able to enter, as is indicated with flow arrow 30, into thefilter cavity 20 if a low pressure is present therein in comparison tothe airspace of the tank 2. So long is this is not the case, ureasolution can flow according to the geodetic pressure, via the wet partof the filter medium 12 into the filter cavity 20, and exit via thesuction connection 22. However, in the event that during operation thevolume flow flowing out via the filter medium 12 falls to less than thepossibly required suction volume of the associated pump, low-pressuredevelops in the filter cavity 20, such that air is suctioned out of theairspace of the tank 2 into the filter cavity 20, the filter cavity issuctioned empty of the clean-side urea solution, and the suctioned airis conveyed within the system. Consequently, safe operation isguaranteed only if the filling level height 28 remains above the elementupper edge 16, which means that not the entire fill quantity of the tankis usable.

FIGS. 3 through 6 show the functionality of the device according to theinvention, which differs from the prior art shown in FIGS. 1 and 2. Inthe invention, the filter element 34, which is disposed on the bottom 10of the tank 2, as in the prior art shown in FIGS. 1 and 2, and isprovided for suction filtration, has a filter medium 32, which isair-impermeable for low suction pressures. Further unlike the prior art,the suction connection 22 in the exemplary embodiment shown in FIGS. 3through 6 is not located at the lower base plate 14 of the filterelement 34, but rather at the upper cover plate 18. FIG. 3 illustrates astate of the device prior to start-up of the system and when filling thetank 2 to a filling level height 28 above the filter element 34. Aquantity of air initially located in the filter cavity 20 before astart-up of the downstream pump device remains enclosed in the filtercavity 20 due to the air-impermeability of the filter medium 34, suchthat during the filling process, an overpressure develops due togeodetic pressure of the urea solution in the filter cavity 20surrounding the filter element 34, such that merely a low bottom layer36 of inflowing urea solutions is formed, above which a quantity of airis located, see FIG. 3. If, starting from the state shown in FIG. 3, thesystem is put into operation, this quantity of air is then dischargedout of the filter cavity 20 by the associated pump, see arrow 38.

To carry out a ventilation operation in the head-side arrangement of thesuction connection 22 by means of the pump device, for example by meansof a self-ventilating pump, the entire air content is discharged fromthe filter cavity 20, until the cleaned fluid initially forming only thebottom layer 36 in the cavity, has risen to the level of the suctionconnection 22. The filter element 34 is now free of air, and the deviceis ready for operation. This state is shown in FIG. 4.

FIGS. 5 and 6 show further phases of operation with a filling levelheight 28 lowered to different degrees. The filter cavity 20 remainsfilled completely with the cleaned urea solution, i.e. free of air, dueto the air-impermeability of the filter medium 34. Therefore, the entirefill quantity of the tank 2 can be used without the danger of airentering into the system, see FIG. 6 showing the state of thepractically completely emptied tank 2.

While the invention is described above based on a device provided forthe suction filtration of an aqueous urea solution (Adblue), it isunderstood that the invention can be applied equally advantageously forother fluids, for which a suction filtration absent the danger of airentry is required. As already mentioned, the ventilation process can becarried out automatically subsequent to a filling. A melt-blown fibermaterial can be advantageously used as a filter medium 32 particularlysuited for the invention. Such a filter medium 32, having a wallthickness of approximately 5 mm and a filter fineness in the range of 10μm, is distinguished by a high capillary effect, such that even withonly partial wetting with a fluid, such as an aqueous urea solution, itis completely sucked full over the entire length thereof, and is thusair-impermeable for the relevant low suction pressures. Whereas thesuction filtration occurs by means of a respective suction pump (notshown) connected to the suction connection 22, it is understood thatdownstream pump devices may be provided as pressure boosters in order togenerate desired operating pressures, for example, injection pressuresfor Adblue applications.

1. A device for the suction filtration of fluids, such as urea solutionsfor exhaust gas after-treatment systems, comprising a tank (2) storingthe fluid, and a filter element (4) disposed therein, provided with afilter medium (12), which separates the tank contents from a clean-sideinner filter cavity (20) and which extends from the bottom area (10) ofthe tank (2) to a filling level height (28), which corresponds to a partof the filling volume of the tank (2), wherein a suction connection (22)is provided on the filter cavity (20) via which the cleaned fluid can bedischarged by way of a suction pressure corresponding to a systemoperating pressure, characterized in that the filter element (34) has afilter medium (32), which is air-impermeable if suction pressures liewithin the range of a low system operating pressure.
 2. The deviceaccording to claim 1, characterized in that the suction connection (22)is disposed on the filter cavity (20) at the upper end thereof remotefrom the tank bottom (10).
 3. The device according to claim 1,characterized in that the filter medium (32) has a melt-blown fibermaterial.
 4. The device according to claim 1, characterized in that thefilter medium (32) has plastic fibers made, in particular, of PA
 66. 5.The device according to claim 1, characterized in that the filter medium(32) has a wall thickness in the range of 2 mm to 10 mm, preferably 5mm, and fineness in the range of 5 μm to 30 μm, preferably 10 μm.
 6. Afilter element for use with a device for suction filtration according toclaim 1, characterized in that it has a filter medium (32), which isair-impermeable for low suction pressures.
 7. The filter elementaccording to claim 6, characterized in that at a clean-side inner filtercavity (20), there is a suction connection (22) that is arranged at theend of the filter cavity (20) which lies removed from the bottom (10) ofa tank (2) accommodating the filter element (34).